SLAPD-LDAP(5)

NAME
slapd-ldap - LDAP backend to slapd

SYNOPSIS
/etc/openldap/slapd.conf

DESCRIPTION
The LDAP backend to slapd(8) is not an actual database; instead it acts as a proxy to forward incoming requests to another LDAP server. While processing requests it will also chase referrals, so that referrals are fully processed instead of being returned to the slapd client.

Sessions that explicitly Bind to the back-ldap database always create their own private connection to the remote LDAP server. Anonymous sessions will share a single anonymous connection to the remote server. For sessions bound through other mechanisms, all sessions with the same DN will share the same connection. This connection pooling strategy can enhance the proxy's efficiency by reducing the overhead of repeatedly making/breaking multiple connections.

The ldap database can also act as an information service, i.e. the identity of locally authenticated clients is asserted to the remote server, possibly in some modified form. For this purpose, the proxy binds to the remote server with some administrative identity, and, if required, authorizes the asserted identity. See the idassert-* rules below. The administrative identity of the proxy, on the remote server, must be allowed to authorize by means of appropriate authzTo rules; see slapd.conf(5) for details.

CONFIGURATION
These slapd.conf options apply to the LDAP backend database. That is, they must follow a "database ldap" line and come before any subsequent "backend" or "database" lines. Other database options are described in the slapd.conf(5) manual page.

Note: In early versions of back-ldap it was recommended to always set

    lastmod  off

for every ldap and meta database. This is because operational attributes related to entry creation and modification should not be proxied, as they could be mistakenly written to the target server(s), generating an error. The current implementation automatically sets lastmod to off, so its use is redundant and should be omitted, because the lastmod directive will be deprecated in the future.

uri <ldapurl>
    LDAP server to use. Multiple URIs can be set in in a single ldapurl argument, resulting in the underlying library automatically call the first server of the list that responds, e.g.

    uri "ldap://host/ ldap://backup-host"

    The URI list is space- or comma-separated. This statement is mandatory.

acl-bind bindmethod=simple|sasl [binddn=<simple DN>] [credentials=<simple password>] [saslmech=<SASL mech>] [secprops=<properties>] [realm=<realm>] [authcId=<authentication ID>] [authzId=<authorization ID>]
    Allows to define the parameters of the authentication method that is internally used by the proxy to collect info related to access control. The identity defined by this directive, according to the properties associated to the authentication method, is supposed to have read access on the target server to attributes used on the proxy for ACL checking. The secprops field is currently ignored. There is no risk of giving away such values; they are only used to check permissions. The default is to use simple, with empty binddn and credentials, which means that the related operations will be performed anonymously.

    This identity is by no means implicitly used by the proxy when the client connects anonymously. See the idassert-bind feature instead. This directive obsoletes acl-authcDN, and acl-passwd.

idassert-bind bindmethod=none|simple|sasl [binddn=<simple DN>] [credentials=<simple password>] [saslmech=<SASL mech>] [secprops=<properties>] [realm=<realm>] [authcId=<authentication ID>] [authzId=<authorization ID>] [authz={native|proxyauthz}] [mode=<mode>] [flags=<flags>]
    Allows to define the parameters of the authentication method that is internally used by the proxy to authorize connections that are authenticated by other databases. The identity defined by this directive, according to the properties associated to the authentication method, is supposed to have auth access on the target server to attributes used on the proxy for authentication and authorization, and to be allowed to authorize the users. This requires to have proxyAuthz privileges on a wide set of DNs, e.g. authzTo=dn.subtree:"", and the remote server to have authz-policy set to to or both. See slapd.conf(5) for details on these statements and for remarks and drawbacks about their usage. The supported bindmethods are

    none|simple|sasl

    where none is the default, i.e. no identity assertion is performed.

    The authz parameter is used to instruct the SASL bind to exploit native SASL authorization, if available; since connections are cached, this should only be used when authorizing with a fixed identity (e.g. by means of the authzDN or authzID parameters). Otherwise, the default proxyauthz is used, i.e. the proxyAuthz control is added to all operations.

    The supported modes are:

    <mode> := {legacy|anonymous|none|self}

    If <mode> is not present, and authzId is given, the proxy always authorizes that identity. <authorization ID> can be

    u:<user>

    [dn:]<DN>

    The former is supposed to be expanded by the remote server according to the authz rules; see slapd.conf(5) for details. In the latter case, whether or not the dn: prefix is present, the string must pass DN validation and normalization.

    The default mode is legacy, which implies that the proxy will either perform a simple bind as the authcDN or a SASL bind as the authcID and assert the client's identity when it is not anonymous. Direct binds are always proxied. The other modes imply that the proxy will always either perform a simple bind as the authcDN or a SASL bind as the authcID, unless restricted by idassert-authzFrom rules (see below), in which case the operation will fail; eventually, it will assert some other identity according to <mode>. Other identity assertion modes are anonymous and self, which respectively mean that the empty or the client's identity will be asserted; none, which means that no proxyAuthz control will be used, so the authcDN or the authcID identity will be asserted. For all modes that require the use of the proxyAuthz control, on the remote server the proxy identity must have appropriate authzTo permissions, or the asserted identities must have appropriate authzFrom permissions. Note, however, that the ID assertion feature is mostly useful when the asserted identities do not exist on the remote server.

    Flags can be

    override,{prescriptive|non-prescriptive}

    When the override flag is used, identity assertion takes place even when the database is authorizing for the identity of the client, i.e. after binding with the provided identity, and thus authenticating it, the proxy performs the identity assertion using the configured identity and authentication method.

    When the prescriptive flag is used (the default), operations fail with inappropriateAuthentication for those identities whose assertion is not allowed by the idassert-authzFrom patterns. If the non-prescriptive flag is used, operations are performed anonymously for those identities whose assertion is not allowed by the idassert-authzFrom patterns.

    This directive obsoletes idassert-authcDN, idassert-passwd, idassert-mode, and idassert-method.

idassert-authzFrom <authz-regexp>
    if defined, selects what local identities are authorized to exploit the identity assertion feature. The string <authz-regexp> follows the rules defined for the authzFrom attribute. See slapd.conf(5), section related to authz-policy, for details on the syntax of this field.

proxy-whoami {NO|yes}
    Turns on proxying of the WhoAmI extended operation. If this option is given, back-ldap will replace slapd's original WhoAmI routine with its own. On slapd sessions that were authenticated by back-ldap, the WhoAmI request will be forwarded to the remote LDAP server. Other sessions will be handled by the local slapd, as before. This option is mainly useful in conjunction with Proxy Authorization.

rebind-as-user {NO|yes}
    If this option is given, the client's bind credentials are remembered for rebinds when chasing referrals. Useful when chase-referrals is set to yes, useless otherwise.

chase-referrals {YES|no}
    enable/disable automatic referral chasing, which is delegated to the underlying libldap, with rebinding eventually performed if the rebind-as-user directive is used. The default is to chase referrals.

tls {[try-]start|[try-]propagate}
    execute the start TLS extended operation when the connection is initialized; only works if the URI directive protocol scheme is not ldaps://. propagate issues the Start TLS exop only if the original connection did. The try- prefix instructs the proxy to continue operations if start TLS failed; its use is highly deprecated.

t-f-support {NO|yes|discover}
    enable if the remote server supports absolute filters (see draft-zeilenga-ldap-t-f for details). If set to discover, support is detected by reading the remote server's root DSE.

BACKWARD COMPATIBILITY
The LDAP backend has been heavily reworked between releases 2.2 and 2.3; as a side-effect, some of the traditional directives have been deprecated and should be no longer used.

server <hostname[:port]>
    this directive is no longer supported. Use the uri directive as described above.

acl-authcDN <administrative DN for access control purposes>
    DN which is used to query the target server for acl checking; it is supposed to have read access on the target server to attributes used on the proxy for acl checking. There is no risk of giving away such values; they are only used to check permissions. The acl-authcDN identity is by no means implicitly used by the proxy when the client connects anonymously. See the idassert-* feature instead. This directive is obsoleted by acl-bind, and may dismissed in the future.

acl-passwd <password>
    Password used with the acl-authcDN above. This directive is obsoleted by acl-bind, and may be dismissed in the future.

idassert-authcDN <administrative DN for proxyAuthz purposes>
    DN which is used to propagate the client's identity to the target by means of the proxyAuthz control when the client does not belong to the DIT fragment that is being proxied by back-ldap. This directive is obsoleted by idassert-bind, and may be dismissed in the future.

idassert-passwd <password>
    Password used with the idassert-authcDN above. This directive is obsoleted by idassert-bind, and may be dismissed in the future.

idassert-mode <mode> [<flags>]
    defines what type of identity assertion is used. This directive is obsoleted by idassert-bind, and may be dismissed in the future.

idassert-method <method> [<saslargs>]
    This directive is obsoleted by idassert-bind, and may be dismissed in the future.

suffixmassage, map, rewrite*
    These directives are no longer supported by back-ldap; their functionality is now delegated to the rwm overlay. Essentially, add a statement

    overlay rwm

    first, and prefix all rewrite/map statements with rwm- to obtain the original behavior. See slapo-rwm(5) for details.

ACCESS CONTROL
The ldap backend does not honor all ACL semantics as described in slapd.access(5). In general, access checking is delegated to the remote server(s). Only read (=r) access to the entry pseudo-attribute and to the other attribute values of the entries returned by the search operation is honored, which is performed by the frontend.

OVERLAYS
The LDAP backend provides basic proxying functionalities to many overlays. The chain overlay, described in slapo-chain(5), and the translucent overlay, described in slapo-translucent(5), deserve a special mention.

Conversely, there are many overlays that are best used in conjunction with the LDAP backend. The proxycache overlay allows caching of LDAP search requests (queries) in a local database. See slapo-pcache(5) for details. The rwm overlay provides DN rewrite and attribute/objectClass mapping capabilities to the underlying database. See slapo-rwm(5) for details.

FILES

/etc/openldap/slapd.conf
    default slapd configuration file

SEE ALSO
slapd.conf(5), slapd-meta(5), slapo-chain(5), slapo-pcache(5), slapo-rwm(5), slapo-translucent(5), slapd(8), ldap(3).

AUTHOR
Howard Chu, with enhancements by Pierangelo Masarati